In a system to which a plurality of power supply devices having a plurality of storage batteries are connected in parallel and which supplies power to a load, a major problem is that the plurality of storage batteries are degraded. The storage batteries are degraded with use history and the amount of energy that can be stored is reduced. Therefore, there is proposed a technique for suppressing the degradation of the plurality of storage batteries by controlling the amount of energy supplied from the storage batteries (that is, the amount of power supplied from the plurality of power supply devices to a load) for each of the storage batteries when the plurality of power supply devices having storage batteries are connected in parallel and power is supplied to a load (for example, PTL 1).